1. Field of the Invention
This invention relates generally to techniques and devices for tracking eye movement, and more specifically to a method and apparatus for sensing electro-oculogram (EOG) signals produced by eye movement and processing those signals to determine the horizontal and vertical position of each eye as well to determine convergence or divergence of the eyes. The signals representing eye position are interfaced to an output device for strabismus measurement or for controlling a video game or other electronic device.
2. Description of the Background Art
Over the past several years interactive video games have gained widespread popularity. Stand-alone game units have been installed in arcades, restaurants, movie theaters, and other publicly accessible facilities. Additionally, video game units have entered the home entertainment market in the form of adapters for standard television sets. As technology has progressed, there has been interest in "virtual reality" where video games take on a three-dimensional character. These games, however, require the use of the hands in their operation thereby making hand/eye coordination essential to successful play. By using movement of the eyes alone to play the game, a higher degree of realism can be achieved.
Several types of systems have been developed over the years to permit computers or machinery to be controlled by eye movement. For example, U.S. Pat. No. 3,462,604 issued to Mason on Aug. 19, 1969, discloses an oculometer for determining eye orientation based on light reflected from the retina of the eye relative to light reflected from the front surface of the eye. Light is directed to the eyeball where it is reflected by both the front surface and the retina at the back of the eye. A detecting system views the reflected images and determines eye position from the relative positions of the reflected images.
U.S. Pat. No. 4,109,145 issued to Graf on Aug. 22, 1978, discloses an apparatus for "line of sight" detection of eye orientation. Using an oculometer or other line of sight determining device to monitor the orientation of the eye, the apparatus measures the length of time that the operator's eye remains in the line of sight position relative to a particular control function. If the line of sight position is maintained longer than a predetermined time, the apparatus produces a control output.
U.S. Pat. No. 3,986,030 issued to Teltscher on Oct. 12, 1976, discloses an eye-motion operable keyboard accessory for paraplegics or other incapacitated persons. The apparatus includes a light source for directing light toward the operator's eye and a plurality of light responsive sensors which are activated by light reflected from the operator's eye. The sensors are connected to a keyboard actuated instrument to be controlled by the eye movement.
U.S. Pat. No. 4,081,623 issued to Vogeley on Mar. 28, 1978, discloses the use of a light source, a radiation sensor, a command discriminator and a display unit to detect when the operator blinks his eyes in a particular coded sequence. The eye blinking is decoded and used to dial a telephone or control a piece of machinery.
U.S. Pat. No. 3,507,988 issued to Holmes on Apr. 21, 1970, discloses a narrow-band television system which has resolution characteristics similar to those of the human eye and which is capable of highly resolving a portion of the transmitted field, the location of which is variable in accordance with the line of sight of an observer. Eye position is determined through the use of reflected light.
U.S. Pat. No. 3,724,932 issued to Cornsweet et al. on Apr. 3, 1973, discloses an apparatus wherein the eye is flooded with light so that a plurality of Purkinje images are formed by the reflecting surfaces of the eye. Two of the Purkinje images are monitored by imaging them on a rotating disc which has a plurality of orthogonal slits through which the Purkinje images are further imaged on a photodetector. The orientation of the optic axis of the eye is determined by monitoring the separation of the Purkinje images.
U.S. Pat. No. 4,866,229 issued to Scharfenberg on Sep. 12, 1989, discloses an apparatus for projecting optical information to a headset so that the wearer can view images which are separate from or superimposed on the directly visible surrounding view.
U.S. Pat. No. 4,651,145 issued to Sutter on Mar. 17, 1987, discloses an oculo-encephalographic communication system in which visual stimuli with unique code signals is presented to the operator and the electro-encephalographic (EEG) signal of the operator is monitored. The code can be identified by the EEG signal of the operator and, therefore, a character on a display can be selected simply by looking at it.
U.S. Pat. No. 4,576,184 issued to Westerman on Mar. 18, 1986, discloses an apparatus for detecting drug ingestion based upon the corneo-retinal potential and/or brain waves using an electro-nystagmograph (ENG) machine.
The disadvantage of many of the systems disclosed in the foregoing patents is that they use light reflected from the eye and are susceptible to interference from other light sources. Other systems require particular visual stimuli to be presented to the operator and corresponding reaction codes to be monitored.
The deficiencies in the foregoing devices can be overcome by using electro-oculogram signals, which represent an electrical signature of eye movement. Co-pending application Ser. No. 07/077,733 filed on Jul. 24, 1987, now Ser. No. 07/784,147, discloses methods and apparatus for using electro-oculogram and other biopotential signals to generate music and to control video devices. Co-pending application Ser. No. 07/557,205 filed on Jul. 24, 1990, discloses methods and apparatus for using electro-oculogram and other biopotential signals to control the cursor on a video display or to operate a video game by merely looking at a particular position on the video display. In these methods and apparatus, however, electro-oculogram signals are generated by eye movement when the eyes are aligned and, in effect, present two-dimensional movement (left/right and up/down). They do not have three-dimensional movement capability or the capability to determine the exact position of each eye independently with relation to a fixed point of reference. See also, Hugh S. Lusted and R. Benjamin Knapp, "Music Produced by Human Bioelectric Signals," presented to the 155th Meeting of the American Association for the Advancement of Science, San Francisco, Calif. on Jan. 18, 1989.
Strabismus, which is a medical condition wherein the eyes do not maintain horizontal or vertical alignment when they are moved, is difficult to measure with accuracy. In order to diagnose the degree of strabismus, it is necessary to determine the position of each eye independently in relation to a fixed reference point. The present invention provides accurate measurement of the position of each eye.
The foregoing patents and publications reflect the state of the art of which the applicant is aware and are tendered with the view toward discharging applicants' acknowledged duty of candor in disclosing information which may be pertinent in the examination of this application. It is respectfully stipulated, however, that none of these patents or publications teach or render obvious, singly or when considered in combination, applicants' claimed invention.